Cause of terrapin die-off unknown

Monday

Jul 13, 2015 at 6:15 AM

Severe winter cold speculated as possible cause

By Rich Eldredreldred@wickedlocal.com

WELLFLEET -- There’s trouble in Turtletown.

Dr. Barabara Brennessel, author of "Diamonds in the Marsh," was strolling along Chipman’s Cove on April 15, checking to see if there were any signs of diamondback terrapins emerging from their winter brumation in the marsh to feed or mate. Instead, she found 10 dazed or dead turtles washed up along the wrack line. In the next three days nine more turned up.

“Then tons of people started calling in,” said Rebecca Shoer, Terrapin Field Coordinator at Mass Audubon's Wellfleet Bay Wildlife Sanctuary.

The turtles, who are native to Wellfleet and spend every winter dug into the mud in Cape Cod Bay, normally should’ve been paddling about happily as the sun warmed the shallow marsh creeks.

“They were lethargic and unresponsive,” noted Shoer. “Turtles were coming up dead and showed symptoms similar to (cold-stunned) sea turtles but nothing like we’d seen before with terrapins. The vast majority were sexually mature females.”

All told, 89 turtles were found in bad shape or dead; one juvenile, 64 mature and 12 unknown as to age. More inexplicably, 76 of the 89 turtles were females; only six were male and seven were too small to identify.

“You can’t lose that many nesting females and not have an impact, we hated to lose those,” sanctuary Director Bob Prescott said. “A nest might have as many as 40 eggs but we’re in a better position to absorb the loss with the turtle gardens and many more volunteers.”

Forty-two turtles washed up dead. Six of the live ones later died.

“They were massively dehydrated, their eyes were sunken. They were lethargic and showed rear muscle paralysis. The legs were not functioning. They had extremely low blood platelet counts which is something we see in hibernating turtles to make circulation easier,” Shoer explained. “But that something was killing them. They were essentially hemorrhaging from the eyes.”

Their blood was so thin it wasn’t clotting. Other were hemorrhaging internally. The live turtles were shipped to Tufts Veterinary School where several died.

“Some terrapins are recovering (at Tufts) and their blood work is fine but they still can’t use their back legs,” Shoer noted.

What happened and why is still a mystery.

“They just got up too early. The photoperiod said 'wake up' and it was way too cold,” Prescott speculated. “The folks at Tufts are finding their blood was thinned for brumation and they didn’t get a chance to thicken it up. The turtles at Tufts have sloughing scales and skin lesions.”

But there could be other reasons.

“At the end of April we got word of terrapin mortality on Long Island and in Delaware Bay. But that’s odd for cold stunning. We think their turtles started to eat snails and got red tide but it is still unclear,” Prescott said.

The most likely explanation was a bad winter.

“It was a pretty mild winter for awhile then it got frigid in February,” Shoer recalled. “Typically they dig deeper when it gets colder. It could be the temperature plunged and they were trapped in the ice (in the bay). It could be the salinity in the area they hibernate, there was so much ice in the bay – the salinity increases (in the remaining water) and it was still so cold in the water in the bay and harbor in April.”

The ice floes scrapping the sea floor might have disrupted the hibernation churning up clumps of turtles.

“It definitely seems like the perfect storm,” Shoer said. “There’s no clear way to know what caused this massive die-off.”

And why would females be hit harder?

“It could be they wake up first because they've got to eat as much calcium as they can to lay their clutch of eggs in June or they brumate in a different place and their mud bank warms up quicker,” Prescott reflected. “We just don’t know enough about their natural history. We can go back through the data and see if we always see females come out early.”

The nesting season, which is under way, has been erratic. Some locations such as Lieutenant Island and Old Wharf Road are seeing very few nesting turtles. The effect on the overall population is hard to gauge.

“There could be upwards of a few thousand in the bay,” Shoer said. “We don’t have an exact estimate. We’ve never done a full mark and recapture. Two dead terrapins washed up in Truro.”

That was actually good news in a way since no one was aware the terrapins occurred there. Wellfleet Bay was perceived as their northern terminus.

“This is probably an annual event when you have a winter like this at the northern edge of their range,” Prescott ventured. “They got caught (in the cold) and that will knock them back a bit but the population is larger (now) so they can take more of a hit.”

It’s a hit no one wants to see again.

“Hopefully, El Nino kicks in and we don’t have another winter like last winter,” Prescott said. “We’ve never had mass cold-stunned event with diamondback terrapins before.”